Multiple edge enabled patterning

ABSTRACT

Provided is an alignment mark having a plurality of sub-resolution elements. The sub-resolution elements each have a dimension that is less than a minimum resolution that can be detected by an alignment signal used in an alignment process. Also provided is a semiconductor wafer having first, second, and third patterns formed thereon. The first and second patterns extend in a first direction, and the third pattern extend in a second direction perpendicular to the first direction. The second pattern is separated from the first pattern by a first distance measured in the second direction. The third pattern is separated from the first pattern by a second distance measured in the first direction. The third pattern is separated from the second pattern by a third distance measured in the first direction. The first distance is approximately equal to the third distance. The second distance is less than twice the first distance.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. Technological advances in IC materials and design have producedgenerations of ICs where each generation has smaller and more complexcircuits than the previous generation. However, these advances haveincreased the complexity of processing and manufacturing ICs and, forthese advances to be realized, similar developments in IC processing andmanufacturing are needed. In the course of integrated circuit evolution,functional density (i.e., the number of interconnected devices per chiparea) has generally increased while geometry size (i.e., the smallestcomponent (or line) that can be created using a fabrication process) hasdecreased.

To achieve small geometry sizes and small pitch sizes, traditionalsemiconductor fabrication processes have used multiple photomasks topattern a wafer. The use of multiple photomasks increases fabricationcosts and prolongs fabrication time. In addition, alignment and overlayerrors may become a greater concern, particularly as geometry sizescontinue to shrink. Moreover, it may be difficult to form both arelatively large pattern and a relatively small pattern on a wafer atthe same time. The large pattern may “disappear” or lose its shape undersome existing fabrication techniques.

Therefore, while existing semiconductor fabrication methods to achievesmall geometry sizes and small pitch sizes have been generally adequatefor their intended purposes, they have not been entirely satisfactory inevery aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 is a flowchart illustrating a method for patterning asemiconductor device according to various aspects of the presentdisclosure.

FIG. 2 is a diagrammatic fragmentary top level view of a portion of aphotomask containing an alignment mark according to various aspects ofthe present disclosure.

FIGS. 3-6 are diagrammatic fragmentary top level views of a portion of awafer containing an alignment mark that corresponds to the alignmentmark of FIG. 2 according to various aspects of the present disclosure.

FIGS. 7-8 are diagrammatic fragmentary top level views of a portion of awafer containing an alternative alignment mark according to variousaspects of the present disclosure.

FIGS. 9-13 are diagrammatic fragmentary top level views of a portion ofa wafer that is undergoing various patterning stages according tovarious aspects of the present disclosure.

FIGS. 14A-14E are diagrammatic fragmentary top level views of a portionof a design layout that help illustrate certain design rules accordingto various aspects of the present disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Moreover,the formation of a first feature over or on a second feature in thedescription that follows may include embodiments in which the first andsecond features are formed in direct contact, and may also includeembodiments in which additional features may be formed interposing thefirst and second features, such that the first and second features maynot be in direct contact. Various features may be arbitrarily drawn indifferent scales for the sake of simplicity and clarity.

Illustrated in FIG. 1 is a flowchart of a method 20 for patterning asemiconductor device. The method 20 begins with block 30 in which afirst pattern is formed on a wafer. The first pattern extends in a firstdirection. The method 20 continues with block 40 in which a secondpattern is formed on the wafer. The second pattern extends in the firstdirection and is separated from the first pattern by a first distancemeasured in a second direction perpendicular to the first direction. Themethod 20 continues with block 50 in which a third pattern is formed onthe wafer. The third pattern is separated from the first pattern by asecond distance measured in the first direction. The third pattern isseparated from the second pattern by a third distance measured in thefirst direction. The first distance is approximately equal to the thirddistance. The second distance is less than twice the first distance.

FIG. 2 is a diagrammatic fragmentary top view of a portion of aphotomask 100. The photomask. The photomask 100 is operable to project aplurality of patterns or images (not illustrated in FIG. 2) to asemiconductor wafer in a photolithography process. The patternscorrespond to different portions of one or more semiconductor devices.The semiconductor device(s) may include an integrated circuit (IC) chip,system on chip (SoC), or portion thereof, and may include variouspassive and active microelectronic devices such as resistors,capacitors, inductors, diodes, metal-oxide semiconductor field effecttransistors (MOSFET), complementary metal-oxide semiconductor (CMOS)transistors, bipolar junction transistors (BJT), laterally diffused MOS(LDMOS) transistors, high power MOS transistors, or other types oftransistors.

In the embodiment illustrated in FIG. 2, the photomask 100 includes analignment mark 110. The alignment mark 110 has two portions 120 and 121that are spaced apart from one another. An outer profile of each of theportions 120-121 of the alignment mark 110 substantially resembles anelongated rectangle that extends in an X-direction.

A plurality of bars (or segments) 130-145 divide (in the X-direction)each of the portions 120-121 into a plurality of smaller rectangular“boxes”. Each of the bars has a dimension 150 measured in a Y-directionthat is perpendicular to the X-direction. It is understood that theX-direction may be a horizontal direction, and the Y-direction may be avertical direction. Alternatively, the X-direction may be a verticaldirection, and the Y-direction may be a horizontal direction. It is alsounderstood that the number of bars 130-145 is arbitrary, and that analternative number of bars may be disposed within (and divide) theportions 120-121 of the alignment mark 110 in alternative embodiments.

The dimension 150 is relatively small. The dimension 150 has a valuesuch that patterns formed on the wafer corresponding to the bars 130-145cannot be individually recognized or detected by an alignment signalused in an alignment process. Alternatively stated, the patterns on thewafer corresponding to the bars 130-145 will be sub-resolution patternsor sub-resolution elements, because they each have a dimension that isless than the minimum resolution that can be detected by the alignmentsignal. This will be discussed in more detail later. The patterns on thephotomask 100 are much larger than the corresponding patterns formed onthe wafer, but their dimensions are directly correlated. Therefore, thedimension 150 is X times the minimum resolution that can be detected bythe alignment signal. X measures a shrinkage in size as image of thepatterns (such as the alignment mark 110) on the photomask 100 aretransferred to a wafer.

In an embodiment, the dimension 150 is associated with a criticaldimension (CD) of a particular semiconductor fabrication technologygeneration/node. The critical dimension represents the smallest featuresize that can be formed on a substrate in the given semiconductorfabrication technology generation. For example, in a 22-nm fabricationtechnology generation, the critical dimension is 22 nm, meaning that thesmallest semiconductor feature that the 22-nm technology generation canform is approximately 22 nm. It is understood, however, that the actualvalue of the dimension 150 may be larger than the value of the criticaldimension, since the dimension 150 represents the critical dimensionwith respect to the photomask 100, which is shrunk when it is patternedonto a semiconductor wafer. For instance, the dimension 150 on thephotomask 100 may be approximately X times the value of the criticaldimension of patterns formed on the wafer.

Under existing semiconductor fabrication techniques, oftentimes a largepattern will “disappear” when it is formed along with small patterns atthe same time. Here, the alignment mark 110 is designed to have theshape and geometry as illustrated in FIG. 2 to solve the problem of“disappearing large patterns”. This will also be discussed in moredetail later.

FIGS. 3-5 are diagrammatic fragmentary top level views of a portion of asemiconductor wafer 200 at various stages of fabrication. Referring nowto FIG. 3, the wafer 200 is a silicon wafer. In an embodiment, the wafer200 is doped with a P-type dopant such as boron. In another embodiment,the wafer 200 is doped with an N-type dopant such as phosphorous orarsenic. The wafer 200 may alternatively be made of some other suitableelementary semiconductor, such as diamond or germanium; a suitablecompound semiconductor, such as silicon carbide, indium arsenide, orindium phosphide; or a suitable alloy semiconductor, such as silicongermanium carbide, gallium arsenic phosphide, or gallium indiumphosphide. Further, the wafer 200 could include an epitaxial layer (epilayer), may be strained for performance enhancement, and may include asilicon-on-insulator (SOI) structure.

The wafer 200 is patterned using the photomask 100 of FIG. 2. Thus, analignment mark 210 is formed on the wafer 200. The alignment mark 210 ismade of a photoresist material. In other words, the alignment mark 210is formed by depositing a layer of photoresist on the wafer 200 througha suitable process, such as a spin coating process, and thensubsequently transferring the image of the alignment mark 110 of thephotomask to the wafer 200 using a suitable photolithography process.The photolithography process may include one or more exposing,developing, baking, and ashing processes.

As a result of the photolithography process, the alignment mark 210 isformed. The alignment mark 210 on the wafer 200 is a resized image ofthe alignment mark 110 on the photomask 100. In an embodiment, thealignment mark 210 has a substantially identical image of the alignmentmark 110 but X times smaller. Thus, the alignment mark 210 includesportions 220 and 221 that each take on a substantially rectangularprofile. The portions 220-221 are divided into boxes by bars 230-245that each extend in the X-direction.

The bars 230-245 each have a dimension 250 that is measured in theY-direction. As discussed above, the dimension 250 is small enough sothat the bars 230-245 cannot be individually detected by an alignmentsignal in an alignment process. In other words, the bars 230-245 aresub-resolution elements, since they each have a dimension 250 that issmaller than the minimum resolution that can be detected by thealignment signal.

The alignment mark 210 also includes elongated bars (or segments)255-258 that each extend in the Y-direction. The bars 255-258 each havea dimension 259 that is measured in the X-direction. The dimension 259is smaller than the minimum resolution that can be detected by thealignment signal. Therefore, the bars 255-258 are also sub-resolutionelements.

In an embodiment, the bars 230-237 are substantially evenly spaced apartfrom one another in the Y-direction, the bars 238-245 are substantiallyevenly spaced apart from one another in the Y-direction.

Referring now to FIG. 4, a spacer film 260 is formed over and around thealignment mark 210. The spacer film 260 is formed by a depositionprocess known in the art, such as chemical vapor deposition (CVD),physical vapor deposition (PVD), atomic layer deposition (ALD),combinations thereof, or another suitable technique. The spacer film 260includes a dielectric material, such as an oxide material, a nitridematerial, an oxy-nitride material, or another suitable material.

In an embodiment, the spacer film 260 is formed in a manner so that athickness of the spacer film 260 approaches, or is approximately equalto, the critical dimension of a given fabrication technology generation.The spacer film 260 is formed over other portions of the wafer 200 as apart of a spacer patterning technique, in which spacers are utilized toachieve the formation of small patterns having small pitches. Forexample, the reduced pitch size achieved by the spacer patterningtechnique may be ½ of the previous pitch size. Hence, the spacerpatterning technique is referred to as a “pitch-halving” process, and isdescribed in more detail in patent application Ser. No. 12/370,152 filedon Feb. 12, 2009, and published on Aug. 12, 2010, U.S. PublicationNumber 2010-0203734A1, the entire content of which is herebyincorporated by reference.

The spacer film 260 is then etched to expose the photoresist material ofthe alignment mark 210. At this point, the spacer film 260 becomesindividual spacers that are disposed all around the various segments ofthe alignment mark 210, such as the bars 230-245 (shown in FIG. 3).These spacers each have a width 270 that is equal to the thickness ofthe spacer film 260, which approaches or is substantially equal to thecritical dimension of the given semiconductor technology generation.

In the embodiment shown in FIG. 4, the spacers inside each of theportions 220-221 of the alignment mark 210 form trenches (or openings),for example, a trench 280. The shape and geometry of the alignment mark210 (and thus the alignment mark 110 on the photomask 100, shown in FIG.2) is designed in a manner so that each of the trenches such as thetrench 280 has a dimension 290 that is measured in the Y-direction. Thedimension 290 has a value that is small enough so that the trenches suchas the trench 280 are considered sub-resolution patterns. In otherwords, the trench 280 cannot be individually recognized or discerned byan alignment signal used in an alignment process.

It is understood, however, that in alternative embodiments, thealignment mark 210 may be designed and formed in a manner so that thetrenches like the trench 280 will disappear altogether. Alternativelystated, the spacers 260 may merge together in a manner so that the“boxes” of the alignment mark 210 are completely filled by the spacermaterial.

Referring now to FIG. 5, the photoresist material is removed using aphotoresist removal process known in the art, such as an ashing or astripping process. The spacers 260 remain after the removal of thephotoresist material. At this stage of fabrication, each of the portions220-221 of the alignment mark 210 includes a plurality of small “boxes”formed by the spacer material. In addition to the trenches (such as thetrench 280) inside these boxes, the removed photoresist material ineffect forms openings 300 in the portions 220-221.

The opening 300 includes a plurality of trench segments that extend inboth the X-direction and the Y-direction. The trench segments of theopening 300 each have a dimension 310. The dimension 310 may be measuredin the X-direction or the Y-direction. As was the case for the trench280, the dimension 310 is small enough so that the trench segments ofthe opening 300 are considered sub-resolution patterns, meaning thatthese trench segments cannot be individually recognized or detected byan alignment signal in an alignment process. In an embodiment, thedimension 310 is substantially equal to the dimensions 250 and 259(shown in FIG. 3).

The alignment mark 210 can be used to align a semiconductor wafer and aphotomask during a photolithography process. As discussed above, analignment mark used under existing methods may have large dimensions,and may disappear when it is formed at the same time as smallerpatterns. As an example, the spacer patterning technique referencedabove may be used to achieve small device geometries and pitch sizes.However, this technique will result in the disappearance of asignificant portion of the alignment mark. For instance, instead ofhaving one or more large rectangles as an intended shape, an alignmentmark may have two much smaller line patterns (spacers) located at topand bottom edges of the rectangle, thereby destroying the intended shapeof the alignment mark.

To address this problem, previous patterning techniques have used anadditional photomask to cover up (or protect) portions of the wafercontaining the alignment mark during the formation of the smallpatterns. However, that approach increases fabrication costs andfabrication time due to the extra photomask and the additionalpatterning process.

In comparison, the alignment mark 210 discussed herein offers advantagesover existing alignment marks. It is understood, however, that otherembodiments of the alignment mark fabricated within the spirit of thepresent disclosure may offer different advantages, and that noparticular advantage is required for all embodiments. One advantage isthat the alignment mark 210 will not disappear in a spacer patterningtechnique. The alignment mark 210 has a shape that resembles rectanglesbeing segmented into much smaller portions (sub-resolution patterns).Since the trench segments of the openings 300 and the trenches such asthe trench 280 are sub-resolution patterns, they will not be detected bythe alignment signal in the alignment process. Thus, the opening 300 andthe trenches such as the trench 280 essentially disappear when viewed bythe alignment signal. The alignment signal will then “treat” or “view”the alignment mark 210 as two large rectangles having shapes defined bythe outer profile of the portions 220 and 221. Refer to FIG. 6 for analignment mark 210A that the alignment signal “thinks” it sees insteadof the alignment mark 210 of FIG. 5.

Another advantage is that, since the alignment mark 210 will notdisappear for the reasons discussed above, no extra photomask oradditional patterning process is required (to cover up the alignmentmark 210) when the spacer patterning technique is carried out. Thislowers fabrication costs and reduces fabrication time.

The alignment mark 210 can be used to pattern a material layertherebelow and form an alignment mark in that material layeraccordingly. Also, although the trenches illustrated in FIG. 5 areformed in a manner so that they mostly extend in the X or Y directions,in alternative embodiments, they may be formed to extend in otherdirections. In other words, the alignment mark 210 may be segmented inan X-direction, a Y-direction, a direction different from both the X andY directions, or combinations thereof. As such, sub-resolution features(with respect to an alignment signal) may be created in any one of thesedirections.

To further illustrate how an alignment mark can be segmented toeliminate the “disappearing large pattern” problem, shown in FIG. 7 is adiagrammatic fragmentary top view of an overlay mark 410 on a wafer 400.The overlay mark 410 has a “box-in-box” structure and is used forprocess monitor in a metrology measurement process. In more detail, theoverlay mark 410 has an inner box 420 and an outer box 430. The innerbox 420 and the outer box 430 may belong to different layers on asemiconductor wafer. The shape and geometry of the overlay mark 410 arethe shape and geometry that a measurement signal is supposed to detectand recognize in a metrology measurement tool.

However, the overlay mark 410 (specifically the outer box 430) may havedimensions that are large enough, such that the “disappearing largepattern” problem discussed above with reference to FIGS. 2-5 may occurwhen the overlay mark 410 is formed using the same processes of thespacer patterning technique referenced above. When that happens, theoverlay mark 410 will no longer take on the shape and geometry displayedin FIG. 7. For example, the outer box 430 may be formed to be two thinrectangular boxes, one inside the other, with an opening separating thetwo rectangular boxes.

To prevent that problem from occurring, the overlay mark 410 (inparticular, the outer box 430) can be segmented in a manner similar tothat discussed above in association with the alignment mark 210 of FIGS.2-5. The segmented overlay mark 410 is shown in FIG. 8.

The outer box 430 is segmented into six (or more) rectangular boxes440-445, wherein each of the boxes 440-445 contains a spacer material.The boxes 440-445 are separated by trenches 450-454 (or openings) thateach have a rectangular shape. The trenches 450-454 are formed byremoving a photoresist material that occupied the trenches 450-454. Inother words, the boxes 440-445 are spacers formed around the photoresistmaterial, and the subsequent removal of the photoresist material resultsin the formation of the trenches 450-454. The spacer-forming process andthe photoresist-removal process are the same processes used in thespacer patterning technique referenced above, which is used to patternfeatures elsewhere on the wafer 400 to achieve the “pitch-halving”discussed in the patent application with the Ser. No. 12/370,152.

The trenches 450-454 each have a dimension 460 in the X-direction and inthe Y-direction. The value of the dimension 460 is small enough to beconsidered sub-resolution patterns with respect to a measurement signalof an alignment process. Thus, the trenches 450-454 will not be detectedor recognized by the measurement signal. To the measurement signal, itis as if the trenches 450-454 do not exist. Consequently, the boxes440-445 are collectively recognized by the measurement signal as theouter box 430 (shown in FIG. 7).

Therefore, the overlay mark 410 requires no additional photomask toprotect it when the spacer patterning technique is carried out. Thesegmentation of the outer box 430 of the overlay mark 410 allows for thespacer patterning technique to be performed with respect to the overlaymark 410 without protection for the overlay mark 410. Since the overlaymark 410 is designed so that the openings 450-454 formed therein willnot be recognized by the measurement signal, the “disappearing largepattern” problem is prevented.

The spacer patterning technique referenced above that is used to achievesmaller pitches between semiconductor patterns also has a “line-end”issue. In more detail, the spacer patterning technique involves formingspacers around line patterns (such as photoresist line patterns), andthen using the spacers as hard masks to pattern features therebelow.However, since the spacers are formed all the way around the linepatterns—meaning that each of the line patterns is surrounded by a“ring” of spacers—the spacers around the end portions of the linepatterns will need to be removed, otherwise they may cause shortingbetween semiconductor features patterned by the adjacent spacers.

To eliminate the “line-end” problem discussed above, traditionalsemiconductor fabrication processes have used one or more additionalphotomasks and photolithography processes to “crop” off the portions ofthe spacers surrounding the end portions of the line patterns. This isreferred to as “line-end cropping”, and it will cause the “ring” ofspacers to be transformed into two adjacent “lines.” However, theadditional photomask and photolithography process increases fabricationcosts and lengthens fabrication time. Furthermore, as discussed above,traditional spacer patterning techniques may need extra photomasks andphotolithography processes to prevent the “disappearing large pattern”problem.

The present disclosure involves a cheaper and more efficient method tosolve the “line-end” problem without using extra masks. The presentdisclosure also helps eliminate the “disappearing large pattern”problem. One of the embodiments of the method of the present disclosureis discussed below and illustrated in FIGS. 9-11.

FIGS. 9-11 are diagrammatic fragmentary top level views of a portion ofa semiconductor wafer 500 at various stages of patterning. Referring toFIG. 9, a plurality of patterns 510-518 are formed on the wafer 500. Thepatterns 510-518 each include a photoresist material in the presentembodiment, but may include other materials in alternative embodiments.

As illustrated in FIG. 9, the patterns 510-517 are relatively smallpatterns and each have a dimension 520 that is measured in theY-direction. In an embodiment, the dimension 520 has a value that isapproximately equal to a critical dimension of a given semiconductorfabrication technology generation. The pattern 518 is a relatively largepattern and includes a dimension 530 that is measured in theY-direction. In an embodiment, the dimension 530 is substantiallygreater than the dimension 520. Thus, the pattern 518 may be used toform large patterns on the wafer 500. For example, the pattern 518 maybe used to form input/output (I/O) devices (or a portion thereof), oralignment marks (or a portion thereof).

In an embodiment, the patterns 510-517 are separated from one another inthe Y-direction by a distance 540, and the pattern 517 and 518 areseparated from each other in the Y-direction by a distance 545. In anembodiment, the distance 540 is approximately equal to the sum of: acritical dimension of a fabrication technology generation and twice thethickness of a spacer formed in the spacer patterning technique. Thedistance 545 is less than, or equal to, the sum of twice the thicknessof a spacer formed in the spacer patterning technique.

Dummy patterns 550 and 551 are formed near the end portions (in theX-direction) of the patterns 510-518. The dummy patterns 550-551 areformed in the same fabrication process that forms the patterns 510-518and may each include a photoresist material. The dummy patterns 550-551are each spaced apart from the patterns 510-518 by a distance 560. In anembodiment, the distance 560 is less than twice the thickness of aspacer formed in the spacer patterning technique. The dummy patterns550-551 help eliminate the “line-end” problem, as will be discussed inmore detail below.

Referring now to FIG. 10, a spacer film 570 is formed on the wafer 500.The spacer film 570 is formed by a suitable deposition process known inthe art, such as CVD, PVD, ALD, or combinations thereof. The spacer film260 includes a dielectric material, such as an oxide material, a nitridematerial, an oxy-nitride material, or another suitable material. Thespacer film 570 is then etched to form spacers 570. The spacers 570surround each of the patterns 510-518. The spacers 570 are formed as apart of the spacer patterning technique referenced above. The spacers570 each include a spacer thickness 580 that approaches, or isapproximately equal to, the critical dimension of a given fabricationtechnology generation.

As discussed above with reference to FIG. 9, the distance 560 separateseach of the dummy patterns 550-551 from the patterns 510-518. Thedistance 560 is less than twice the spacer thickness 580. As a result,the spacers 570 between the dummy patterns 550-551 and the patterns510-518 will merge into each other, leaving no gaps therebetween. Also,since the distance 545 (shown in FIG. 9) between the dummy pattern 518and the pattern 517 is less than twice the spacer thickness 580, thespacers 570 between the dummy pattern 518 and the pattern 517 will alsomerge together.

Meanwhile, recall that the distance 540 (shown in FIG. 9) that separatesthe patterns 510-517 from one another is approximately equal to the sumof: a critical dimension of a fabrication technology generation andtwice the spacer thickness 580. Therefore, the spacers 570 formedbetween the patterns 510-517 will not merge together, and instead willdefine boundaries of trenches 590-596, along with the spacers 570 formedaround the dummy patterns 550-551. In other words, the spacers 570formed between the patterns 510-517 define the edges of the trenches590-596 in the X-direction, and a portion of the spacers 570 formedaround the dummy patterns 550-551 define the edges of the trenches590-596 in the Y-direction. These trenches 590-596 each have a dimension600 that is measured in the Y-direction. The dimension 600 isapproximately equal to the critical dimension of a fabricationtechnology generation.

Referring now to FIG. 11, the photoresist material of the patterns510-517 as well as the photoresist material of the dummy patterns550-551 are removed in a suitable process, such as an ashing process ora stripping process. The removal of the photoresist material transformsthe patterns 510-517 and the dummy patterns 550-551 into trenches(openings) 510-517 and 550-551.

At this stage of fabrication, the trenches 510-517 and the trenches590-596 essentially have been “pitch-halved” compared to the patterns510-517 in FIG. 9. The trenches 510-517 and 590-596 can be used topattern semiconductor elements therebelow, and therefore may be referredto as device patterns. For example, if a trench pattern (for example, ametal line) is desired, then the trenches 510-517 and 590-596 can beused to form these trench patterns directly to the material layertherebelow.

If a line pattern (for example, a gate line) is desired, then adeposition process can be used to fill the trenches 510-517 and 590-596with a material, for example with a hard mask material. The hard maskmaterial is different from the spacer material of the spacers 570 (thatdefine the boundaries of the trenches 510-517 and 590-596). For example,the hard mask material and the spacers 570 may have a different etchingselectivity. Thereafter, the spacers 570 can be removed, and then thehard mask material filling the openings 510-517 and 590-596 can then beused as hard mask patterns to form the desired line patterns in thematerial layer therebelow.

Therefore, the embodiment discussed above in FIGS. 9-11 accomplishes thepitch-halving objective of the spacer patterning technique withoutneeding additional masks to perform “line-end cropping.” Thehalf-pitched patterns were the spacers (after “line-end cropping” isperformed) according to the spacer patterning technique. In comparison,the embodiment disclosed herein uses the trenches 510-517 and 590-596 asthe half-pitched patterns. Since the trenches 510-517 and 590-596 arealready completely separated from one another, there is no need to do“line-end cropping” (there is no potential shorting between the featuresto be patterned by the trenches 510-517 and 590-596). In addition, thedimensions of the trenches 510-517 and 590-596 are approximately equalto the critical dimension. Therefore, very small features can bepatterned by the trenches 510-517 and 590-596 in addition to achievingthe pitch-halving objective.

From the above discussions, it can be seen that one of the advantagesoffered by the embodiment discussed with reference to FIGS. 9-11 is amore efficient and cheaper patterning process. The trenches 510-517 and590-596 can be used to pattern the wafer and require no “line-endcropping”, and yet they are able to achieve the same objectives of thespacer patterning techniques discussed previously.

Another advantage offered by the embodiment discussed with reference toFIGS. 9-11 is that it eliminates the “disappearing large pattern”problem. As illustrated in FIG. 11, the large pattern 518 may become alarge trench 518, but it still retains its original shape and geometryafter the smaller trenches 510-517 are formed. A deposition process maybe utilized to fill the large trench 518 so as to create a large patternafter the spacers 570 are removed. In other words, the pattern 518 maybe restored through a “reverse process”. As discussed previously, thislarge pattern 518 can be used to pattern an alignment mark, an I/Odevice, or portions thereof.

FIGS. 12-13 illustrate another example showing how dummy patterns can beused to resolve the “line-end” cropping issue. FIGS. 12-13 arediagrammatic fragmentary top level views of a portion of a semiconductorwafer 700 at various stages of patterning. Referring to FIG. 12, aplurality of patterns 710-720 are formed on the wafer 700. The patterns710-720 each include a photoresist material in the present embodiment,but may include other materials in alternative embodiments.

The patterns 710-714 are desired patterns, which may also be referred toas device patterns. For example, the patterns 710-714 may be used laterto form lines (such as gate lines) or trenches (such as trenches formetal interconnect lines). The patterns 715-720 are dummy patterns andare used to help eliminate the “line-end cropping” issue. Spacers730-740 are formed around the patterns 710-720, respectively.

The placement/location of the dummy patterns 715-720 are chosen in amanner such that trenches 750-754 are defined by the spacers 730-740.For example, the spacers defining the boundaries of the trenches 750-754are merging into the adjacent spacers, or at least coming into contactwith the adjacent spacers. This ensures that no undesired holes oropenings are inadvertently formed. In more detail, the trench 750 isformed by the spacers 735 (defining an upper boundary), 732 (defining alower boundary), 736 (defining a left boundary), and 730 (defining aright boundary). Similarly, the trench 751 is formed by the spacers 735,733, 730, and 731; the trench 752 is formed by the spacers 735, 734,731, and 737; the trench 753 is formed by the spacers 730, 740, 732, and733; the trench 754 is formed by the spacers 731, 740, 733, and 734. Thedesign rules governing the placement of the dummy patterns will bediscussed in more detail later with reference to FIGS. 14A-14E.

Referring back to FIG. 12, the patterns 710-715 each have a lateraldimension 770, and the trenches 750-754 each have a lateral dimension775. The lateral dimensions 770 and 775 are measured in the X-directionand may each approach a critical dimension associated with asemiconductor fabrication technology generation. In an embodiment, thelateral dimensions 770 and 775 are substantially equal, and the trenches750-754 are respectively aligned along the Y-direction with the patterns712, 710, 713, 711, and 714.

Referring now to FIG. 13, the patterns 710-720 are removed. Therefore,the patterns 710-720 become trenches 710-720. The trenches 710-714 aredesired trenches, which may thereafter be used to form trench patternsin a layer therebelow. The trenches 715-720 are dummy trenches, whichmay or may not be used to pattern anything thereafter.

It can be seen now that the trenches 750 and 712 appear as if they werea single trench that has been cut in the middle to become two trenches.The same can be said for the trenches 710 and 753, the trenches 751 and713, the trenches 711 and 754, and the trenches 752 and 714. Intraditional processes, an extra mask may be required to cut theline/trench patterns into two (or more) separate line/trench patterns aswell. This extra mask may be the same mask as the mask used to carry outthe “line-end cropping.”

In comparison, the dummy patterns 715-720 here are formed so that theirspacers 735-740 touch or merge into the spacers 730-734 of the patterns710-714. Thus, the trenches 750-754 are “constrained” by these spacers730-740. The “line-end” problem is obviated in this fashion. Inaddition, no extra mask is required to cut these trenches. This meansthat only a single mask and is needed to pattern the wafer 700 in adesired manner using only a single patterning process.

FIGS. 14A-14E help illustrate some design rules regarding the formationof the dummy patterns and the spacers discussed above with reference toFIGS. 9-13. Referring to FIG. 14A, top level views of example polygons800-802 are shown. The polygons 800-802 are the layout patterns used toform the desired line/trench patterns. It is understood that a layoutmay contain a plurality of polygons that are similar to the polygons800-802, though they may be different in shape. One of the design rulesis that for the spacers around the polygons 800-802 to merge, thespacing between adjacent polygons should be less than or equal to twicethe spacer sidewall thickness. In FIG. 14A, the spacer sidewallthickness is designated with reference numeral 810, and the spacingbetween adjacent polygons is designated with reference numeral 815. Thisdesign rule ensures that no undesired empty openings/holes will beformed by the spacers, and that the spacers will form the desired trenchopenings instead.

Referring to FIG. 14B, top level views of example polygons 820-824 areshown. The spacers (not illustrated) that will be formed around thepolygons 820-824 will result in the formation of example trenches 830and 831, whose boundaries are shown as broken lines in FIG. 14B. Some ofthe design rules illustrated by FIG. 14B include:

-   The smaller polygons (such as the polygons 820-821) have a dimension    that is substantially equal to a critical dimension target    associated with a semiconductor fabrication technology generation.    This dimension is designated with reference numeral 840 in FIG. 14B.    In an embodiment, the dimension 840 may be in a range from about 20    nm to about 40 nm.-   The spacer sidewall thickness is also substantially equal to the    critical dimension target associated with the semiconductor    fabrication technology generation. In other words, the spacer    sidewall thickness may be equal to the dimension 840 of the    polygons. The spacer sidewall thickness is designated with reference    numeral 841 in FIG. 14B.-   A pitch between adjacent polygons is less or equal to about four    times the spacer sidewall thickness 841 or the dimension 840 of the    polygons. The pitch is designated with reference numeral 842 in FIG.    14B. In an embodiment, the pitch 842 is in a range from about 80 nm    to about 160 nm.

As FIG. 14B illustrates, the trenches 830-831 is surrounded byextensions of polygons 820-824. The extension may be in a range fromabout 20 nm to about 40 nm. This is a different way of saying that thespacer sidewall thickness is in a range from about 20 nm to about 40 nm.

FIG. 14C illustrates a portion of a proper layout that meets the designrules discussed above. As FIG. 14C shows, a trench 850 is fullysurrounded by spacers 855, leaving no undesired holes or openings.

FIGS. 14D-14E each illustrate a portion of an improper layout that doesnot meet the design rules discussed above. As FIG. 14D shows, thespacers 860 form a trench 865, but only a smaller trench 870 is desired.In other words, the trench 865 encompasses and is bigger than thedesired trench 870. As a result, an undesired opening/hole is created bythe improper layout shown in FIG. 14D.

Referring to FIG. 14E, the spacers 880 form a trench 885, when no trenchis supposed to be formed. Thus, the entire trench 885 is an undesiredhole/opening. The improper layouts shown in FIGS. 14D-14E violate thedesign rules and may cause problems in fabrication, and therefore shouldbe avoided.

It is understood that the embodiments illustrated in FIGS. 2-13 anddiscussed above are merely examples of the concept contained within thepresent disclosure. Other embodiments may be implemented that carry outthe trench forming process differently. For example, in alternativeembodiments, additional dummy patterns or differently shaped dummypatterns may be used to help define the boundaries of the trenches.Also, the technique to eliminate the “disappearing large pattern”problem discussed above with reference to FIGS. 2-8 may be implementedand carried out along with the embodiment illustrated in FIGS. 9-13.

One of the broader forms of the present disclosure involves an alignmentmark. The alignment mark includes a plurality of sub-resolutionelements. The sub-resolution elements each have a dimension. Thedimension is a function of a minimum resolution that can be detected byan alignment signal used in an alignment process.

Another of the broader forms of the present disclosure involves asemiconductor device. The semiconductor device includes: a first patternformed on a semiconductor wafer. The first pattern extends in a firstdirection. The semiconductor device includes a second pattern formed onthe wafer. The second pattern extends in the first direction and isseparated from the first pattern by a first distance measured in asecond direction perpendicular to the first direction. The semiconductordevice includes a third pattern formed on the wafer. The third patternis separated from the first pattern by a second distance measured in thefirst direction. The third pattern is separated from the second patternby a third distance measured in the first direction. The first distanceis approximately equal to the third distance. The second distance isless than twice the first distance.

Still another of the broader forms of the present disclosure involves amethod. The method includes forming a first pattern on a wafer. Thefirst pattern extends in a first direction. The method includes forminga second pattern on the wafer. The second pattern extends in the firstdirection and is separated from the first pattern by a first distancemeasured in a second direction perpendicular to the first direction. Themethod includes forming a third pattern on the wafer. The third patternis separated from the first pattern by a second distance measured in thefirst direction. The third pattern is separated from the second patternby a third distance measured in the first direction. The first distanceis approximately equal to the third distance; and the second distance isless than twice the first distance.

The foregoing has outlined features of several embodiments so that thoseskilled in the art may better understand the detailed description thatfollows. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions andalterations herein without departing from the spirit and scope of thepresent disclosure.

1. An alignment mark, comprising: a plurality of sub-resolutionelements; wherein: the sub-resolution elements each have a dimensionthat is a function of a minimum resolution that can be detected by analignment signal used in an alignment process.
 2. The alignment mark ofclaim 1, wherein the dimension of each of the sub-resolution elements issmaller than the minimum resolution that can be detected by thealignment signal.
 3. The alignment mark of claim 1, wherein thealignment mark is formed on a wafer, and wherein the sub-resolutionelements each include an opening that is surrounded by a spacer film. 4.The alignment mark of claim 3, wherein a thickness of the spacer film isapproximately equal to a minimum critical dimension for aphotolithography technology generation.
 5. The alignment mark of claim1, wherein: the sub-resolution elements include a first subset of thesub-resolution elements and a second subset of the sub-resolutionelements; the sub-resolution elements in the first subset each extendsubstantially in a first direction and each have a first dimensionmeasured in a second direction that is perpendicular to the firstdirection; the sub-resolution elements in the second subset each extendsubstantially in the second direction and each have a second dimensionmeasured in the first direction; and the first dimension and the seconddimension are each less than the minimum resolution that can be detectedby the alignment signal.
 6. The alignment mark of claim 1, wherein atleast a portion of the sub-resolution elements are substantially evenlyspaced apart from one another.
 7. The alignment mark of claim 1, whereinthe dimension of each of the sub-resolution elements is approximatelyequal to a minimum critical dimension for a photolithography technologygeneration.
 8. The alignment mark of claim 1, wherein: the alignmentmark is formed on a photomask; and the dimension of each of thesub-resolution elements is less than X times the minimum resolution thatcan be detected by the alignment signal, X measuring size shrinkage asan image of the alignment mark is transferred from the photomask to awafer.
 9. A semiconductor device, comprising: a first pattern formed ona semiconductor wafer, the first pattern extending in a first direction;a second pattern formed on the wafer, the second pattern extending inthe first direction and being separated from the first pattern by afirst distance measured in a second direction perpendicular to the firstdirection; and a third pattern formed on the wafer, the third patternbeing separated from the first pattern by a second distance measured inthe first direction, the third pattern being separated from the secondpattern by a third distance measured in the first direction; wherein:the first distance is approximately equal to the third distance; and thesecond distance is less than twice the first distance.
 10. Thesemiconductor device of claim 9, wherein the first and third distancesare each approximately equal to a spacer thickness.
 11. Thesemiconductor device of claim 9, wherein: the first and second patternsare separated by a spacer; the second and third patterns are separatedby a spacer; and the first and third patterns are separated by twospacers that are merged together.
 12. The semiconductor device of claim9, wherein: the first pattern has a first dimension that is measured inthe second direction; the second pattern has a second dimension that ismeasured in the second direction; the third pattern has a thirddimension that is measured in the first direction; and the first,second, and third dimensions are each approximately equal to a criticaldimension of a semiconductor fabrication technology generation.
 13. Thesemiconductor device of claim 9, wherein the first, second, and thirdpatterns each define a trench.
 14. The semiconductor device of claim 9,wherein: the third pattern is a dummy pattern; and the first and secondpatterns are device patterns.
 15. The semiconductor device of claim 9,further including: a fourth pattern that is separated from the firstpattern by a fourth distance that is measured in the second direction;wherein: the fourth distance is less than twice a spacer thickness; anda dimension of the fourth pattern measured in the second direction issubstantially greater than dimensions of the first and second patternsmeasured in the second direction.
 16. A method, comprising: forming afirst pattern on a wafer, the first pattern extending in a firstdirection; forming a second pattern on the wafer, the second patternextending in the first direction and being separated from the firstpattern by a first distance measured in a second direction perpendicularto the first direction; and forming a third pattern on the wafer, thethird pattern being separated from the first pattern by a seconddistance measured in the first direction, the third pattern beingseparated from the second pattern by a third distance measured in thefirst direction; wherein: the first distance is approximately equal tothe third distance; and the second distance is less than twice the firstdistance.
 17. The method of claim 16, wherein the forming the firstpattern and the forming the third pattern each include: forming a linepattern having a photoresist material; forming spacers around the linepattern; and removing the line pattern, thereby defining a first trenchas the first pattern and defining a second trench as the third pattern;wherein edges of the first and second trenches are defined by thespacers.
 18. The method of claim 17, further including: forming a fourthpattern that is similar to the first pattern and that extends in thefirst direction; and forming a fifth pattern that is similar to thethird pattern and that is separated from the first pattern by the seconddistance in the first direction; wherein: the third and fifth patternsare disposed on opposite sides of the first pattern; and the secondpattern is formed by defining a trench that is constrained by spacersformed around the first, third, fourth, and fifth patterns.
 19. Themethod of claim 16, wherein the first and third distances are eachapproximately equal to a spacer thickness.
 20. The method of claim 16,further including: forming a fourth pattern that is separated from thefirst pattern by a fourth distance that is measured in the seconddirection; wherein: the fourth distance is less than twice a spacerthickness; a dimension of the fourth pattern measured in the seconddirection is substantially greater than dimensions of the first andsecond patterns measured in the second direction; and the third patternis a dummy pattern.